Electrolytic capacitor and manufacturing method therefor

ABSTRACT

An electrolytic capacitor includes a capacitor element, and a liquid solution with which the capacitor element is impregnated. The capacitor element includes: an anode foil having a dielectric layer thereon, and a cathode layer including a conductive polymer and in contact with the dielectric layer. The liquid solution contains at least one of polyalkylene glycol and derivatives thereof. A total weight content of polyalkylene glycol and derivatives thereof in the liquid solution is 15 wt % or greater with respect to a weight of the liquid solution.

BACKGROUND

1. Technical Field

The present disclosure relates to an electrolytic capacitor used invarious electronic apparatuses.

2. Background Art

With digitalization of electronic apparatuses, there is a demand forcapacitors having a small size, a large capacitance, and a smallequivalent series resistance (hereinafter, abbreviated as “ESR”) in ahigh frequency region to be used at a power supply output side ofcircuits such as, for example, a smoothing circuit and a controlcircuit. As such capacitors, electrolytic capacitors using a fluidelectrolyte typically such as an electrolyte solution have been used.Furthermore, recently, solid electrolytic capacitors using a solidelectrolyte such as manganese dioxide, a TCNQ complex salt, or anelectroconductive polymer such as polypyrrole, polythiophene, andpolyaniline have been used.

The solid electrolytic capacitor is excellent in that it has aparticularly low ESR as compared with a liquid-type electrolyticcapacitor. However, the solid electrolytic capacitor is poor inrepairing a defective part in anodic oxide film as a dielectric body.Therefore, leakage current may increase, and, in the worst case, a shortcircuit may occur.

Meanwhile, particularly, in recent AV apparatuses and automobileelectrical equipment, high reliability has been increasingly demanded.Therefore, also in solid electrolytic capacitors, low leakage currentand a short-circuit resistance property, in addition to performance suchas having a small size, a large capacitance, and a low ESR, are beingdemanded. In order to meet such demands, a so-called hybrid-typeelectrolytic capacitor using an electrolyte solution, as material for anelectrolyte, that is excellent in repairing a defective part in ananodic oxide film that is a dielectric body in addition to a solidelectrolyte such as an electroconductive polymer has been proposed.

FIG. 4 is a sectional view showing a configuration of a hybrid-typeelectrolytic capacitor (having wound-type capacitor element) as anexample of conventional electrolytic capacitor. FIG. 5 is a developmentperspective view of a capacitor element of the hybrid-type electrolyticcapacitor. As shown in FIG. 4, the hybrid-type electrolytic capacitorincludes capacitor element 2 as a function element, a pair of lead wires1A and 1B, and outer package 5. One end portion of each of lead wires 1Aand 1B is connected to capacitor element 2. Outer package 5 enclosescapacitor element 2 and an electrolyte solution (not shown) in such amanner that the other end portion of each of lead wires 1A and 1B is ledto the outside.

Outer package 5 includes bottomed cylindrical case 3 and seal member 4.Case 3 accommodates capacitor element 2 impregnated with the electrolytesolution. Seal member 4 is provided with through holes 4A and 4B throughwhich lead wires 1A and 1B are inserted, respectively. Seal member 4 iscompressed by drawing processing part 3A provided on the outerperipheral surface of case 3 so as to seal an opening of case 3. Sealmember 4 is made of rubber packing.

As shown in FIG. 5, capacitor element 2 includes anode foil 2A, cathodefoil 2B, and separator 2C. Anode foil 2A is formed by roughing a foilmade of a valve metal such as aluminum by etching, and forming an anodicoxide film (not shown) as a dielectric body thereon by anodization.Cathode foil 2B is formed of a valve metal such as aluminum. Separator2C is disposed between anode foil 2A and cathode foil 2B. In this state,anode foil 2A, cathode foil 2B and separator 2C are laminated and woundso as to form capacitor element 2. A solid electrolyte layer (not shown)made of an electroconductive polymer such as polythiophene is formedbetween anode foil 2A and cathode foil 2B.

One end portion of lead wire 1A is connected to anode foil 2A, and oneend portion of lead wire 1B is connected to cathode foil 2B. The otherend portions thereof are led out from one end surface of capacitorelement 2.

The electrolyte solution includes a solvent, a solute, and additives,and it is based on an electrolyte solution that has been used in aconventional liquid-type electrolytic capacitor using only a liquidelectrolyte. The liquid-type electrolytic capacitors are roughlyclassified into electrolytic capacitors having a low withstand voltagein which a rated voltage is not greater than 100 W.V. and having a lowESR, and electrolytic capacitors having a high withstand voltage inwhich a rated voltage is, for example, 250 W.V., 350 W.V., and 400 W.V.Mainly, the former electrolytic capacitors are used in a smoothingcircuit and a control circuit at the power supply output side, and thelatter electrolytic capacitors are used in a smoothing circuit at apower supply input side. These are largely different from each other invarious properties of an electrolyte solution to be used in eachelectrolytic capacitor because roles in the circuit and materialcompositions are different from each other. Therefore, these electrolytesolutions cannot be used compatibly.

On the other hand, the hybrid-type electrolytic capacitor is used in asmoothing circuit and a control circuit at the power supply output sidebecause it has an ESR as low as that of a solid-type electrolyticcapacitor and has a limitation with respect to a withstand voltage.Therefore, a conventional hybrid-type electrolytic capacitor employs anelectrolyte solution having high electric conductivity and an excellentlow-temperature characteristic, which is applicable for conventionalliquid-type electrolytic capacitors. Specific examples of theelectrolyte solution is an electrolyte solution includingγ-butyrolactone, ethylene glycol or the like as a main solvent, andamidine phthalate, tetramethylammonium phthalate, ammonium adipate,triethylamine phthalate or the like as a solute.

In a conventional hybrid-type electrolytic capacitor configured asmentioned above, an electrolyte solution enters into pores in the solidelectrolyte layer of an electroconductive polymer formed in capacitorelement 2, and thus, a contact state between a dielectric oxide film andthe electrolyte is improved. Therefore, the capacitance is increased,the ESR is lowered, repairing of a defective part in the dielectricoxide film is promoted by the effect of the electrolyte solution, andthus leakage current is reduced. Such an electrolytic capacitor isdisclosed in, for example, Japanese Patent Application UnexaminedPublication No. H11-186110 and No. 2008-10657.

Electrolytic capacitors used in AV apparatuses and automobile electricalequipment require high reliability over a long period of time. Suchelectrolytic capacitors are used under a harsh environment at hightemperatures, for example, at a maximum working temperature of 85° C. to150° C. for a long time. Meanwhile, a conventional hybrid-typeelectrolytic capacitor has a configuration in which an opening of a caseaccommodating a capacitor element and an electrolyte solution is sealedby sealing material such as rubber and epoxy resin, and thereforelifetime design becomes important.

However, a solvent of the electrolyte solution used in a conventionalhybrid-type electrolytic capacitor is a volatile organic solvent such asrbutyrolactone, ethylene glycol, and sulfolane. Therefore, when theelectrolytic capacitor is exposed to a high temperature, the solventgradually penetrates into a gap between the seal member and the case, agap between the seal member and the lead wires, or the seal memberitself, and gradually vaporizes and volatilizes. In general, anelectrolytic capacitor is designed to have a guaranteed lifetime suchthat a range in which stable properties can be maintained with variationof the physical properties of material to be used or manufacturingconditions taken into consideration. However, if the electrolyticcapacitor is used for a long time beyond the guaranteed lifetime, asolvent in the electrolyte solution is finally lost. Therefore, afunction of self-repairing a defective part in the dielectric oxide filmis lost.

In a conventional liquid-type electrolytic capacitor using only liquidelectrolyte, even if the solvent of the electrolyte solution is lost,since the dielectric oxide film and the cathode foil are insulated fromeach other by the separator, electrolytic capacitor is only to be in anopen mode and not in a short circuit.

On the other hand, in the hybrid-type electrolytic capacitor, even ifthe solvent of the electrolyte solution is lost, an electroconductivesolid electrolyte layer remains between the dielectric oxide film andthe cathode foil. Therefore, when an effect of the electrolyte solutionis lost, an increase in leakage current is caused. As a result, in aworst case, a short circuit occurs.

SUMMARY

An electrolytic capacitor of an aspect of the present disclosureincludes a capacitor element, and a liquid solution with which thecapacitor element is impregnated. The capacitor element includes: ananode foil having a dielectric layer thereon, and a cathode layerincluding a conductive polymer and in contact with the dielectric layer.The liquid solution includes at least one of polyalkylene glycol andderivatives thereof. A total weight content of polyalkylene glycol andderivatives thereof in the liquid solution is 15 wt % or greater withrespect to a weight of the liquid solution.

An electrolytic capacitor of another aspect of the present disclosureincludes a capacitor element, and a liquid solution with which thecapacitor element is impregnated. The capacitor element includes: ananode foil having a dielectric layer thereon, a cathode layer includinga conductive polymer and in contact with the dielectric layer. Theliquid solution contains at least one of polyethylene glycol andderivatives thereof, both having a mean molecular weight from 300 to1000, inclusive, or at least one of polypropylene glycol and derivativesthereof, both having a mean molecular weight from 200 to 5000,inclusive.

An electrolytic capacitor of still another aspect of the presentdisclosure includes a capacitor element, and a liquid solution withwhich the capacitor element is impregnated. The capacitor elementincludes: an anode foil having a dielectric layer thereon, a cathodelayer including a conductive polymer and in contact with the dielectriclayer. The liquid solution contains at least one of polyalkylene glycoland derivatives thereof. The liquid solution further contains at leastone of diphenyl amine, naphthol, nitrophenol, catechol, resorcinol,hydroquinone, pyrogallol, trimellitic acid, pyromellitic acid, boricacid, boric-acid compounds, phosphoric acid, phosphoric-acid compounds,and complexes of mannitol and boric acid.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing a configuration of a hybrid-typeelectrolytic capacitor (having wound-type capacitor element) of anexample of an electrolytic capacitor in accordance with an exemplaryembodiment of the present disclosure.

FIG. 2 is a developed perspective view of a capacitor element of thehybrid-type electrolytic capacitor shown in FIG. 1.

FIG. 3 is an enlarged conceptual view of a principal part of thecapacitor element shown in FIG. 2.

FIG. 4 is a sectional view showing a configuration of a hybrid-typeelectrolytic capacitor (having wound-type capacitor element) of anexample of a conventional electrolytic capacitor.

FIG. 5 is a developed perspective view of a capacitor element of thehybrid-type electrolytic capacitor shown in FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Firstly, a configuration of an electrolytic capacitor in accordance withthis exemplary embodiment is described with reference to FIGS. 1 and 2.FIG. 1 is a sectional view showing a configuration of a hybrid-typeelectrolytic capacitor (having wound-type capacitor element) of anexample of an electrolytic capacitor in accordance with an exemplaryembodiment of the present disclosure, and FIG. 2 is a developedperspective view of a capacitor element of the hybrid-type electrolyticcapacitor.

As shown in FIG. 1, the electrolytic capacitor includes capacitorelement 12, first lead wire 11A and second lead wire 11B (hereinafter,referred to as “lead wires 11A and 11B”), and outer package 15. As shownin FIG. 2, capacitor element 12 includes anode foil 12A, cathode foil12B, and separator 12C disposed between anode foil 12A and cathode foil12B. Lead wire 11A is connected to anode foil 12A, and lead wire 11B isconnected to cathode foil 12B. That is to say, one end portion of leadwire 11A is connected to anode foil 12A, and one end portion of leadwire 11B is connected to cathode foil 12B. The other end portions oflead wires 11A and 11B are led out from the same end surface ofcapacitor element 12. Outer package 15 encloses capacitor element 12such that the other end portions of lead wires 11A and 11B are led tothe outside.

Outer package 15 includes bottomed cylindrical case 13 and seal member14. Case 13 accommodates capacitor element 12 impregnated with anelectrolyte solution mentioned below. Seal member 14 is provided withthrough holes 14A and 14B through which lead wires 11A and 11B areinserted, respectively. Seal member 14 is disposed at an opening of case13, and is compressed to seal (close) the opening of case 13 when theouter peripheral surface of case 13 is subjected to drawing processingby drawing processing part 13A.

Next, a configuration of the capacitor element is described withreference to FIG. 3. FIG. 3 is an enlarged conceptual view of aprincipal part of the capacitor element shown in FIG. 2. Capacitorelement 12 includes solid electrolyte layer 122 in addition to theabove-mentioned anode foil 12A, cathode foil 12B and separator 12C.Furthermore, capacitor element 12 is impregnated with electrolytesolution 16.

Anode foil 12A is formed by roughing a foil made of a valve metal suchas aluminum by etching, and forming a dielectric anodic oxide filmthereon by anodization. That is to say, anode foil 12A has dielectriclayer 121 on the surface thereof. Cathode foil 12B is formed of a valvemetal such as aluminum. Anode foil 12A and cathode foil 12B arelaminated and wound with separator 12C interposed therebetween.Furthermore, solid electrolyte layer 122 made of an electroconductivepolymer such as polythiophene and derivatives thereof is formed betweenanode foil 12A and cathode foil 12B. That is to say, solid electrolytelayer 122 is in contact with dielectric layer 121 and cathode foil 12B.Solid electrolyte layer 122 is not dense but porous such that there arepores inside thereof, and electrolyte solution 16 enters into the pores.

Note here that capacitor element 12 may be configured by laminating aplurality of anode foils 12A and cathode foils 12B via separators 12C.

Seal member 14 can be made by using resin material such as an epoxyresin in addition to rubber material such as EPT and IIR. Separator 12Ccan be made by using a nonwoven fabric containing cellulose, kraft,polyethylene terephthalate, polybutylene terephthalate, polyphenylenesulfide, nylon, aromatic polyamide, polyimide, polyamide-imide,polyether imide, rayon, and glass.

Electrolyte solution 16 is prepared by dissolving a solute in a solvent.Examples of the solute include an ammonium salt of inorganic acid, anamine salt of inorganic acid, and an alkyl-substituted amidine salt ofinorganic acid or quaternized products thereof, as well as an ammoniumsalt of organic acid, an amine salt of organic acid, and analkyl-substituted amidine salt of organic acid or quaternized productsthereof. Examples of inorganic acid compounds include a boric acidcompound, a phosphoric acid compound, and the like. Examples of organicacid compounds include aliphatic carboxylic acid such as adipic acid,and aromatic carboxylic acid such as phthalic acid, benzoic acid,salicylic acid, trimellitic acid, and pyromellitic acid. Examples ofammonium compounds include ammonia, and dihydroxy ammonium; and examplesof amine compounds include triethyl amine, methyl diethyl amine,trishydroxymethyl amino methane, and the like. Examples of thealkyl-substituted amidine salt or the quaternized products thereofinclude a quaternized product of 1,2,3,4-tetramethyl imidazolinium andcompounds such as 1-ethyl-2,3-dimethyl imidazolinium and1-ethyl-3-methyl imidazolium.

Electrolyte solution 16 includes at least one low-volatile solventselected from polyalkylene glycol and a derivative of polyalkyleneglycol as solvent material. Polyalkylene glycols are substantiallynon-volatile (low-volatile). Specific examples include polyethyleneglycol, polyethylene glycol glyceryl ether or polyethylene glycoldiglyceryl ether or polyethylene glycol sorbitol ether, polypropyleneglycol, polypropylene glycol glyceryl ether, polypropylene glycoldiglyceryl ether, polypropylene glycol sorbitol ether, polybutyleneglycol, copolymers of ethylene glycol and propylene glycol, copolymersof ethylene glycol and butylene glycol, and copolymers of propyleneglycol and butylene glycol. These can be used singly or in combinationof two or more of them.

Furthermore, among polyalkylene glycol or derivatives thereof, inparticular, polyethylene glycol or derivatives thereof hardly evaporatein the below-mentioned acceleration test and, in other words, theyexhibit extremely great low-volatility, when the mean molecular weightis 300 or more. Meanwhile, when the mean molecular weight is more than1000, although the low-volatility is maintained, viscosity is increasedand an effective capacitance rate is lowered, and it is largely loweredparticularly at a low temperature. Therefore, an optimum mean molecularweight is in a range from 300 to 1000, inclusive.

Furthermore, since polypropylene glycol or derivative thereof have alarge propylene structure as a basic unit, they hardly evaporate in thesame acceleration test and exhibit extremely great low-volatility whenthe mean molecular weight is 200 or more. Meanwhile, since the propylenestructure is more hydrophobic than the ethylene structure, the viscositycan be kept low until the mean molecular weight is about 5000.Therefore, the effective capacitance rate of the capacitor at lowtemperature is excellent. However, when the mean molecular weight ismore than 5000, the low volatility is obtained but the viscosity isincreased, and thus the effective capacitance rate of the capacitor islowered and it is largely lowered particularly at a low temperature.Therefore, an optimum mean molecular weight is in a range from 200 to5000, inclusive.

In a single polymerized product (homopolymer) such as polyethyleneglycol or polypropylene glycol, the molecular weight can be controlledeasily at the time of polymerization. Therefore, molecular weightdistribution is stabilized, excellent thermal stability can beexhibited, and the long lifetime can be achieved. Furthermore, in thecase of a polymerized product having a molecular weight of 200 or more,the interaction between molecules becomes stronger and thus the thermalstability is more improved. Therefore, such a polymerized product isoptimum for capacitors having a long guaranteed lifetime.

As mentioned above, an electrolyte solution, which has been used in aconventional hybrid-type electrolytic capacitor used in a smoothingcircuit or a control circuit at the power supply output side, includes avolatile organic solvent such as γ-butyrolactone and ethylene glycol asa solvent. Therefore, if a conventional hybrid-type electrolyticcapacitor is continued to be used under a high-temperature environmentof a maximum working temperature of 85° C. to 150° C. for a long timebeyond the guaranteed lifetime, the solvent of electrolyte solution 16is lost by vaporization and volatilization. As a result, an effect ofrepairing a dielectric oxide film cannot be exhibited.

On the other hand, the electrolytic capacitor in accordance with thisexemplary embodiment includes liquid-state polyalkylene glycol as alow-volatile solvent. This liquid-state polyalkylene glycol hardlyvolatilizes even under a high-temperature environment of a maximumworking temperature of 85° C. to 150° C. Consequently, even if it isused under a high temperature as mentioned above for a long time beyondthe guaranteed lifetime, electrolyte solution 16 can be allowed toremain in capacitor element 12. Therefore, the repairing effect of thedielectric oxide film can be maintained.

Furthermore, the content of polyalkylene glycol or derivatives thereofas the low-volatile solvent in electrolyte solution 16 is 15 wt. % ormore, this low-volatile solvent can cover an entire part of thedielectric oxide film on the surface of anode foil 12A. Furthermore,this low-volatile solvent can move along separator 12C and a solidelectrolyte existing between the dielectric oxide film and cathode foil12B and reach cathode foil 12B. Consequently, defective parts over thedielectric oxide film can be repaired, and thus an extremely excellentshort-circuit resistance property can be exhibited.

As the upper limit of the content of polyalkylene glycol or derivativesthereof, all of the solvent excluding a solute and additives may beliquid state polyalkylene glycol or derivatives thereof.

However, as the impregnation property of electrolyte solution 16 intocapacitor element 12 is taken into consideration, electrolyte solution16 may be prepared by mixing the other solvents, for example,γ-butyrolactone, ethylene glycol, and sulfolane, having volatility andlow viscosity.

Furthermore, solid electrolyte layer 122 is an electroconductive polymersuch as polythiophene or derivatives thereof, for example,poly(3,4-ethylenedioxythiophene). The electroconductive polymerincorporates dopant. The dopant has a role of expressing electricconductivity. As the typical dopant, acids such as p-toluenesulfonicacid and polystyrenesulfonic acid are used.

However, when dedoping proceeds because an electroconductive polymer isexposed to an alkaline atmosphere due to electrolysis of water existingin the surroundings, or because an electroconductive polymer reacts witha base component in electrolyte solution 16, the conductivity may belowered. Thus, it is preferable that the dissolved components such as asolute and additives dissolved in the low-volatile solvent include moreof the acid than the base. Thanks to the more acid, since thesurrounding environment of solid electrolyte layer 122 continues to bemaintained at the acidic state by electrolyte solution 16, dedoping issuppressed, and change in the ESR of the electrolytic capacitor can bereduced. Furthermore, since polyalkylene glycol or derivatives thereofcontinue to remain as the solvent, the solute and the additives cancontinue to exhibit their functions in the solvent.

Examples of acids constituting these dissolved components includearomatic organic carboxylic acid, for example, phthalic acid, benzoicacid, nitrobenzoic acid, salicylic acid, trimellitic acid, andpyromellitic acid. Among them, trimellitic acid and pyromellitic acidcontaining at least three carboxyl groups are particularly preferablebecause they have a larger number of carboxyl groups and can be moreacidic as compared with conventional phthalic acid. Furthermore,inorganic acid such as boric acid and phosphoric acid and compoundsthereof are more stable even at a high temperature. Furthermore, since acomplex of mannitol and boric acid is more acidic, it exhibits a specialadvantageous effect with respect to a dedoping reaction at a hightemperature.

When a strongly acidic solute or additives are used, dedoping can besuppressed efficiently. However, there is a problem that aluminum as anelectrode body is dissolved with the strongly acidic solute oradditives. Therefore, in order to ensure reliability, it is important tocontrol the dedoping reaction by selecting weak acid such as organiccarboxylic acid and boric acid.

Furthermore, electrolyte solution 16 can contain appropriate additivesfor the purpose of absorbing gas, stabilizing a withstand voltage,adjusting pH, preventing oxidization, and the like. For example,polyalkylene glycol and/or derivatives thereof may contain an oxidationinhibitor. As the oxidation inhibitor, amine-based oxidation inhibitors,benzotriazole-based oxidation inhibitors, phenol-based oxidationinhibitors, and phosphorus-based oxidation inhibitors are effective forapplications of use of capacitors. Examples thereof include diphenylamine, naphthol, nitrophenol, catechol, resorcinol, hydroquinone,pyrogallol, and the like. Among them, hydroquinone and pyrogallolinclude a plurality of OH groups, and have a high oxidation inhibitingeffect. Such additives may be used singly or in combination thereof.

Next, a method for manufacturing the electrolytic capacitor configuredas mentioned above in accordance with an exemplary embodiment isdescribed with reference to FIGS. 1 and 2. Firstly, anode foil 12Ahaving dielectric layer 121 of oxide film on the surface thereof andmade of a valve metal such as aluminum, cathode foil 12B and separator12C are cut into a predetermined width and length. Then, one endportions of lead wires 11A and 11B are respectively connected to anodefoil 12A and cathode foil 12B by a method such as caulking, or a methodusing ultrasonic waves. After that, as shown in FIG. 2, anode foil 12Aand cathode foil 12B are wound in a roll form with separator 12Cinterposed therebetween to be formed into an approximately cylindricalshape, and the side surface of the outer periphery is fixed withinsulating tape and the like (not shown). Thus, capacitor element 12 isformed.

Note here that it is preferable that the surface of anode foil 12A issubjected to etching, vapor deposition of metal particles, or the like,so that the surface area of anode foil 12A is appropriately enlarged.Dielectric layer 121 made of an oxide film is formed as a dielectricoxide film by subjecting a valve metal such as aluminum as electrodematerial to anodic oxidation. In addition, dielectric layer 121 may beformed on electrode material by vapor deposition or coating.

Note here that it is preferable that the surface of cathode foil 12 B issubjected to surface treatment such as etching, formation of an oxidefilm, vapor deposition of metal particles, and attachment ofelectrically conductive particles such as carbon, if necessary, in orderto improve the contact state with respect to solid electrolyte layer122.

After that, an oxide film on the surface of anode foil 12A may berepaired by applying a voltage to lead wires 11A and 11B after immersingthe formed capacitor element 12 in an anodization solution.

Next, lead wires 11A and 11B led out from capacitor element 12 areinserted into through holes 14A and 14B provided in seal member 14,respectively, and seal member 14 is mounted on capacitor element 12.Seal member 14 may be mounted before capacitor element 12 is immersed inan anodization solution.

After that, solid electrolyte layer 122 is formed between anode foil 12Aand cathode foil 12B of capacitor element 12. For solid electrolytelayer 122, for example, poly(3,4-ethylenedioxythiophene) (PEDOT) as anelectroconductive polymer is used. In this case, electrolyte layer 122is formed by, for example, allowing capacitor element 12 to beimpregnated with a dispersion solution in which PEDOT is dispersed,followed by lifting up capacitor element 12 and drying thereof.Alternatively, PEDOT may be formed by a chemical polymerization reactionin capacitor element 12 by using a solution of a monomer such as3,4-ethylenedioxythiophene, an oxidizer solution containing ferricp-toluenesulfonate and the like, and ethanol and the like as a solvent,and impregnating capacitor element 12 with these solutions.

Next, capacitor element 12 is accommodated in case 13 together withelectrolyte solution 16 and disposed at an opening of case 13. In orderto allow capacitor element 12 to be impregnated with electrolytesolution 16, a predetermined amount of electrolyte solution 16 ispreviously injected in case 13, and capacitor element 12 is impregnatedwith electrolyte solution 16 when it is accommodated in case 13.Alternatively, capacitor element 12 may be immersed in an impregnationtank storing electrolyte solution 16 and lifted up, and then it may beaccommodated in case 13. Furthermore, the pressure of the surroundingmay be occasionally reduced at the time of impregnation. Note here thatan excess amount of electrolyte solution 16 that cannot be used forimpregnation of capacitor element 12 may be kept in case 13.

Next, drawing processing part 13A is formed by winding and tighteningcase 13 from the outer peripheral side surface, thereby an opening ofcase 13 is sealed. As an outer package, capacitor element 12 is coveredwith an insulating coating resin made of, for example, an epoxy resin,and the other end portions of lead wires 11A and 11B may be led to theouter part of the outer package material.

Furthermore, an electrolytic capacitor may be, for example, a surfacemount type as mentioned below. Firstly, an insulating terminal plate(not shown) is disposed so that it is in contact with an opening of case13. Then, the other end portions of lead wires 11A and 11B led out fromthe outer surface of seal member 14 sealing the opening of case 13 areinserted into a pair of through holes (not shown) provided in theinsulating terminal plate. Then, lead wires 11A and 11B are bent atabout a right angle in mutually different directions and accommodated inrecess portions (not shown) provided on the outer surface of theinsulating terminal plate.

Note here that after the opening of case 13 is sealed, or after theinsulating terminal plate is attached, a voltage may be appliedappropriately between lead wires 11A and 11B, and thus, re-anodizationmay be carried out.

As mentioned above, an electrolytic capacitor in this exemplaryembodiment includes electrolyte solution 16 containing polyalkyleneglycol or derivatives thereof, and solid electrolyte layer 122 of, forexample, an electroconductive polymer. Therefore, an electrolyticcapacitor having a small size, a large capacitance, and a low ESR isachieved. The volatility of polyalkylene glycol or derivatives thereofis extremely low. Therefore, even if the electrolytic capacitor is usedunder a high-temperature environment of a maximum working temperature of85° C. to 150° C. for a long time beyond the guaranteed lifetime,electrolyte solution 16 having an effect of repairing a defective partoccurring in a dielectric oxide film can be continued to be maintained.As a result, in the electrolytic capacitor in this exemplary embodiment,an increase in leakage current is suppressed and an excellentshort-circuit resistance property can be ensured.

Hereinafter, advantageous effects of this exemplary embodiment aredescribed with reference to specific samples E1 to E18.

(Sample E1)

As sample E1 of an electrolytic capacitor in accordance with anexemplary embodiment of the present disclosure, a hybrid-typeelectrolytic capacitor having a wound-type capacitor element (diameter:6.3 mm, height: 5.8 mm, and guaranteed lifetime: 5,000 hours at 105° C.)having a rated voltage of 35 V and a capacitance of 27 μF is prepared.

Firstly, as shown in FIG. 2, anode foil 12A made of aluminum and havingdielectric layer 121 of aluminum oxide film on the surface thereof,cathode foil 12B, and separator 12C are cut into a predetermined widthand length. Then, one end portions of lead wires 11A and 11B arerespectively connected to anode foil 12A and cathode foil 12B byneedle-caulking. After that, anode foil 12A and cathode foil 12B arewound in a roll form with separator 12C interposed therebetween to beformed into an approximately cylindrical shape. Furthermore, the outerperipheral side surface is fixed with insulating tape (not shown). Thus,capacitor element 12 is formed.

Note here that the surface area of anode foil 12A is enlarged by anetching process. Furthermore, dielectric layer 121 made of aluminumoxide film is formed by an anodic oxidation process. Also, the surfacearea of cathode foil 12B is enlarged by an etching process. Note herethat separator 12C is made of a nonwoven fabric mainly containingcellulose.

Next, lead wires 11A and 11B led out from capacitor element 12 areinserted into through holes 14A and 14B provided in seal member 14 ofrubber packing, and seal member 14 is mounted on capacitor element 12.

After that, capacitor element 12 is immersed in an anodization solutionthat is kept at 60° C., a voltage of 63 V is applied between lead wires11A and 11B for 10 minutes, and thus, an oxide film on the surface ofanode foil 12A is repaired.

Next, solid electrolyte layer 122 made ofpoly(3,4-ethylenedioxythiophene) (PEDOT) is formed between anode foil12A and cathode foil 12B of capacitor element 12. Specifically, aftercapacitor element 12 is impregnated with a dispersion solution in whichPEDOT is dispersed in an aqueous solution, capacitor element 12 islifted up and dried at 110° C. for 30 minutes. In the PEDOT, polystyrenesulfonic acid is used as dopant.

On the other hand, various electrolyte solutions shown in Tables 1 to 4are prepared. Among them, electrolyte solution B is injected intobottomed cylindrical case 13 made of aluminum. Electrolyte solution Bcontains ethyldimethylamine phthalate, and 5 wt. % of polyethyleneglycol (molecular weight: 300) as a solvent.

TABLE 1 electrolyte solution PEG (wt %) GBL (wt %) SL (wt %) A 0 50 25 B5 45 25 C 10 40 25 D 15 35 25 E 50 0 25 F 75 0 0 PEG: polyethyleneglycol (molecular weight: 300) GBL: γ-butyrolactone SL: sulfolane * Eachelectrolyte solution contains 24 wt % of ethyldimethylamine phthalateand 1 wt % of nitrobenzoic acid.

TABLE 2 electrolyte molecular weight of solution polyethylene glycol G200 H 400 I 600 J 1000 K 1500 L 2000 * The composition is as following:15 wt % of polyethylene glycol, 35 wt % of γ-butyrolactone, 25 wt % ofsulfolane, 24 wt % of ethyldimethylamine phthalate and 1 wt % ofnitrobenzoic acid.

TABLE 3 electrolyte FEDMA NBA boric acid PA PG solution (wt %) (wt %)(wt %) (wt %) (wt %) M 20 1 4 — — N 20 1 — 4 — O 16 1 — 4 4 FEDMA:ethyldimethylamine phthalate NBA: nitrobenzoic acid PA: pyromelliticacid PG: pyrogallol * Each electrolyte solution contains 15 wt % ofpolyethylene glycol (molecular weight: 300), 35 wt % of -butyrolactoneand 25 wt % sulfolane.

TABLE 4 electrolyte molecular weight of solution polypropylene glycol P100 Q 200 R 5000 S 6000 * The composition is as following: 15 wt % ofpolypropylene glycol, 35 wt % of γ-butyrolactone, 25 wt % of sulfolane,24 wt % of ethyldimethylamine phthalate and 1 wt % of nitrobenzoic acid.

Then, capacitor element 12 is inserted into case 13, capacitor element12 is impregnated with electrolyte solution 16, and seal member 14mounted on capacitor element 12 is disposed at an opening of case 13.

Next, case 13 is wound and tightened from the outer peripheral sidesurface around the opening to form drawing processing part 13A, thusgenerating a compressive stress on seal member 14 that is a rubberelastic body. Thus, an opening of case 13 is sealed.

Thereafter, re-anodization is carried out by applying a voltage of 40 Vbetween lead wires 11A and 11B led out to the outside for 60 minutes.Thus, an electrolytic capacitor of sample E1 is produced.

Relative to the configuration of sample E1, in samples E2 to E18,compositions of the electrolyte solution are changed, and electrolytesolutions C to S shown in Tables 1 to 4 are used, respectively. Insamples E2 to E5 (electrolyte solutions C to F), the ratio (wt. %) ofpolyethylene glycol contained in electrolyte solution 16 is changed. Insamples E6 to E11 (electrolyte solutions G to L), the molecular weightof polyethylene glycol is changed. In samples E12 to E14 (electrolytesolutions M to O), a solute and additives are further added. In samplesE15 to E18 (electrolyte solutions P to S), polyalkylene glycol containedin electrolyte solution 16 is polypropylene glycol, and the molecularweight of polypropylene glycol is changed. Hereinafter, samples E2 toE18 are described in detail.

(Sample E2)

As sample E2, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E1except that electrolyte solution C shown in Table 1 is used instead ofelectrolyte solution B used in sample E1, and electrolyte solution Ccontains ethyldimethylamine phthalate and nitrobenzoic acid and contains10 wt. % of polyethylene glycol (molecular weight: 300) as a solvent.

(Sample E3)

As sample E3, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E1except that electrolyte solution D shown in Table 1 is used instead ofelectrolyte solution B used in sample E1, and electrolyte solution Dcontains ethyldimethylamine phthalate and nitrobenzoic acid and contains15 wt. % of polyethylene glycol (molecular weight: 300) as a solvent.

(Sample E4)

As sample E4, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E1except that electrolyte solution E shown in Table 1 is used instead ofelectrolyte solution B used in sample E1, and electrolyte solution Econtains ethyldimethylamine phthalate and nitrobenzoic acid, andcontains 50 wt. % of polyethylene glycol (molecular weight: 300) as asolvent.

(Sample E5)

As sample E5, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E1except that electrolyte solution F shown in Table 1 is used instead ofelectrolyte solution B used in sample E1, and electrolyte solution Fcontains ethyldimethylamine phthalate and nitrobenzoic acid, andcontains 75 wt. % of polyethylene glycol (molecular weight: 300) as asolvent.

(Sample E6)

As sample E6, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution G shown in Table 2 is used instead ofelectrolyte solution D used in sample E3, and the molecular weight ofpolyethylene glycol is changed from 300 to 200 in electrolyte solution Gas compared with electrolyte solution D.

(Sample E7)

As sample E7, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution H shown in Table 2 is used instead ofelectrolyte solution D used in sample E3, and the molecular weight ofpolyethylene glycol is changed from 300 to 400 in electrolyte solution Has compared with electrolyte solution D.

(Sample E8)

As sample E8, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution I shown in Table 2 is used instead ofelectrolyte solution D used in sample E3, and the molecular weight ofpolyethylene glycol is changed from 300 to 600 in electrolyte solution Ias compared with electrolyte solution D.

(Sample E9)

As sample E9, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution J shown in Table 2 is used instead ofelectrolyte solution D used in sample E3, and the molecular weight ofpolyethylene glycol is changed from 300 to 1000 in electrolyte solutionJ as compared with electrolyte solution D.

(Sample E10)

As sample E10, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution K shown in Table 2 is used instead ofelectrolyte solution D used in sample E3, and the molecular weight ofpolyethylene glycol is changed from 300 to 1500 in electrolyte solutionK as compared with electrolyte solution D.

(Sample E11)

As sample E11, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution L shown in Table 2 is used instead ofelectrolyte solution D used in sample E3, and the molecular weight ofpolyethylene glycol is changed from 300 to 2000 in electrolyte solutionL as compared with electrolyte solution D.

(Sample E12)

As sample E12, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution M shown in Table 3 is used instead ofelectrolyte solution D used in sample E3, and as compared withelectrolyte solution D, electrolyte solution M additionally containsboric acid (4 wt. %) and the weight content of ethyldimethylaminephthalate is reduced by the that of boric acid.

(Sample E13)

As sample E13, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution N shown in Table 3 is used instead ofelectrolyte solution D used in sample E3, and as compared withelectrolyte solution D, electrolyte solution N additionally containspyromellitic acid (4 wt. %) and the weight content of ethyldimethylaminephthalate is reduced by that of pyromellitic acid.

(Sample E14)

As sample E14, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution O shown in Table 3 is used instead ofelectrolyte solution D used in sample E3, and as compared withelectrolyte solution D, electrolyte solution O additionally containspyromellitic acid (4 wt. %) and pyrogallol (4 wt. %), and the weightcontents of ethyldimethylamine phthalate is reduced by that ofpyromellitic acid and pyrogallol.

(Sample E15)

As sample E15, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E3except that electrolyte solution P shown in Table 4 is used instead ofelectrolyte solution D used in sample E3, and polyalkylene glycolcontained in the electrolyte solution is changed from polyethyleneglycol (molecular weight: 300) to polypropylene glycol (molecularweight: 100) in electrolyte solution P as compared with electrolytesolution D.

(Sample E16)

As sample E16, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E15except that electrolyte solution Q shown in Table 4 is used instead ofelectrolyte solution P used in sample E15, and polyalkylene glycolcontained in the electrolyte solution is changed from polypropyleneglycol (molecular weight: 100) to polypropylene glycol (molecularweight: 200) in electrolyte solution Q as compared with electrolytesolution P.

(Sample E17)

As sample E17, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E15except that electrolyte solution R shown in Table 4 is used instead ofelectrolyte solution P used in sample E15, and polyalkylene glycolcontained in the electrolyte solution is changed from polypropyleneglycol (molecular weight: 100) to polypropylene glycol (molecularweight: 5000) in electrolyte solution R as compared with electrolytesolution P.

(Sample E18)

As sample E18, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E15except that electrolyte solution S shown in Table 4 is used instead ofelectrolyte solution P used in sample E15, and polyalkylene glycolcontained in the electrolyte solution is changed from polypropyleneglycol (molecular weight: 100) to polypropylene glycol (molecularweight: 6000) in electrolyte solution S as compared with electrolytesolution P.

Furthermore, electrolytic capacitors are produced for comparison withsamples E1 to E18. Sample C1 is a hybrid-type electrolytic capacitorwhich does not contain polyethylene glycol in an electrolyte solution.Sample C2 is a solid-type electrolytic capacitor which includes a solidelectrolyte of PEDOT as an electrolyte, and which does not includes anelectrolyte solution. Sample C3 is a liquid-type electrolytic capacitorwhich includes only an electrolyte solution that does not containpolyethylene glycol, as an electrolyte. In other words, sample C3 doesnot include a solid electrolyte. Also, sample C3 is configured to beused for electrolytic capacitors having a low withstand voltage in whicha rated voltage is at most 100 W.V. and has a low ESR, which is used ina smoothing circuit and a control circuit at the power supply outputside.

Note here that for comparison, as samples C4 to C7, liquid-typeelectrolytic capacitors, which include, as an electrolyte, only anelectrolyte solution containing polyethylene glycol and which does notinclude a solid electrolyte are produced. Hereinafter, these samples C1to C7 are described.

(Sample C1)

As sample C1, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E1except that electrolyte solution A shown in Table 1 is used instead ofelectrolyte solution B used in sample E1, and as compared withelectrolyte solution B, electrolyte solution A does not containpolyethylene glycol in a solvent and the weight content ofγ-butyrolactone is increased by that of polyethylene glycol.

(Sample C2)

Sample C2 includes only a solid electrolyte made of PEDOT withoutincluding electrolyte solution B used in sample E1. With such aconfiguration, a solid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced.

(Sample C3)

As sample C3, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample E1except that solid electrolyte made of PEDOT used in sample E1 is notincluded and electrolyte solution A shown in Table 1 is used instead ofelectrolyte solution B, and as compared with electrolyte solution B,electrolyte solution A does not contain polyethylene glycol in a solventand the weight content of γ-butyrolactone is increased by that ofpolyethylene glycol.

(Sample C4)

As sample C4, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample C3except that electrolyte solution B shown in Table 1 is used instead ofelectrolyte solution A used in sample C3, and as compared withelectrolyte solution A, electrolyte solution B contains 5 wt % ofpolyethylene glycol in a solvent and the weight content ofγ-butyrolactone is reduced by that of polyethylene glycol.

(Sample C5)

As sample C5, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample C3except that electrolyte solution C shown in Table 1 is used instead ofelectrolyte solution A used in sample C3, and as compared withelectrolyte solution A, electrolyte solution C contains 10 wt % ofpolyethylene glycol in a solvent and the weight content ofγ-butyrolactone is reduced by that of polyethylene glycol.

(Sample C6)

As sample C6, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample C3except that electrolyte solution D shown in Table 1 is used instead ofelectrolyte solution A used in sample C3, and as compared withelectrolyte solution A, electrolyte solution D contains 15 wt % ofpolyethylene glycol in a solvent and the weight content ofγ-butyrolactone is reduced by that of polyethylene glycol.

(Sample C7)

As sample C7, a hybrid-type electrolytic capacitor including awound-type capacitor element and having a rated voltage of 35 V and acapacitance of 27 μF is produced in the same manner as in sample C3except that electrolyte solution E shown in Table 1 is used instead ofelectrolyte solution A used in sample C3, and as compared withelectrolyte solution A, electrolyte solution E contains 50 wt % ofpolyethylene glycol in a solvent and the weight content γ-butyrolactoneis reduced by that of polyethylene glycol.

Configurations of the solid electrolytes and the electrolyte solutionsin the electrolytic capacitors in the above-mentioned samples E1 to E18and samples C1 to C7 are shown in Table 5. Furthermore, 30 samples ofelectrolytic capacitors of each of samples E1 to E18 and samples C1 toC7 are produced, and the initial properties are measured. Themeasurement results are shown in Table 6.

As the initial properties, capacitance values, ESR values, and leakagecurrent values are measured and the average values thereof arecalculated. The capacitance value is measured at 120 Hz, the ESR valueis measured at 100 kHz, and the leakage current value is measured as avalue after the rated voltage is applied for two minutes. Measurement iscarried out in a 20° C. environment.

TABLE 5 solid electrolyte electrolyte sample layer solution remarks E1PEDOT B PEG(Mw300)5 wt % E2 PEDOT C PEG(Mw300)10 wt % E3 PEDOT DPEG(Mw300)15 wt % E4 PEDOT E PEG(Mw300)50 wt % E5 PEDOT F PEG(Mw300)75wt % E6 PEDOT G PEG(Mw200)15 wt % E7 PEDOT H PEG(Mw400)15 wt % E8 PEDOTI PEG(Mw600)15 wt % E9 PEDOT J PEG(Mw1000)15 wt % E10 PEDOT KPEG(Mw1500)15 wt % E11 PEDOT L PEG(Mw2000)15 wt % E12 PEDOT MPEG(Mw300)15 wt % + boric acid E13 PEDOT N PEG(Mw300)15 wt % + PA E14PEDOT O PEG(Mw300)15 wt % + PA + PG E15 PEDOT P PPG(Mw100)15 wt % E16PEDOT Q PPG(Mw200)15 wt % E17 PEDOT R PPG(Mw5000)15 wt % E18 PEDOT SPPG(Mw6000)15 wt % C1 PEDOT A without polyalkylene glycol C2 PEDOT —without electrolyte solution C3 — A without solid electrolyte layer,without polyalkylene glycol C4 — B without solid electrolyte layer,PEG(Mw300)5 wt % C5 — C without solid electrolyte layer, PEG(Mw300)10 wt% C6 — D without solid electrolyte layer, PEG(Mw300)15 wt % C7 — Ewithout solid electrolyte layer, PEG(Mw300)50 wt % PEG: polyethyleneglycol Mw: molecular weight PPG: polypropylene glycol PA: pyromelliticacid PG: pyrogallol PEDOT: poly(3,4-ethylenedioxythiophene)

TABLE 6 initial property sample capacitance (μF) ESR (Ω) leakage current(μA) E1 27.0 0.023 0.5 E2 26.9 0.022 0.6 E3 26.9 0.023 0.5 E4 26.9 0.0210.6 E5 27.0 0.022 0.7 E6 27.1 0.022 0.6 E7 27.0 0.023 0.6 E8 27.0 0.0220.5 E9 26.9 0.023 0.7 E10 24.2 0.021 0.6 E11 23.9 0.023 0.7 E12 27.00.021 0.5 E13 26.8 0.023 0.7 E14 26.9 0.022 0.5 E15 27.0 0.021 0.6 E1627.1 0.022 0.6 E17 26.9 0.023 0.5 E18 24.3 0.022 0.5 C1 26.9 0.023 0.6C2 20.1 0.023 10.1 C3 27.0 2.130 0.7 C4 27.0 2.450 0.8 C5 26.9 2.882 0.6C6 26.8 3.160 0.6 C7 27.0 4.301 0.5

As shown in Table 5, hybrid-type electrolytic capacitors shown insamples E1 to E18 include electrolyte solution 16 containingpolyalkylene glycol or derivatives thereof and a solid electrolyte madeof an electroconductive polymer, as the electrolyte. Therefore, as shownin Table 6, samples E1 to E18 have an ESR that is as low as that ofsample C2 using a solid electrolyte. Furthermore, they exhibit greatercapacitance and an extremely low leakage current property as comparedwith sample C2.

Sample C1 is a hybrid-type electrolytic capacitor including electrolytesolution A that has been used in a conventional liquid-type electrolyticcapacitor having a rated voltage of at most 100 W.V. applicable to asmoothing circuit and a control circuit at the power supply output side.Samples E1 to E18 show the same level of the initial properties ascompared with sample C1.

Note here that electrolyte solutions B to E used in samples E1 to E4contain polyethylene glycol as a solvent. Electrolyte solutions B to Eare also used in samples C3 to C7. As is apparent from the results ofsamples C3 to C7, when electrolyte solutions B to E are used in aconventional liquid-type electrolytic capacitor, an ESR is extremelylarge. Thus, electrolyte solutions B to E cannot be used in liquid-typeelectrolytic capacitors having a low ESR and a low withstand voltage ofa rated voltage of at most 100 W.V. applicable to circuits at the powersupply output side, for example, a smoothing circuit or a controlcircuit.

Next, an acceleration test is carried out for evaluating electrolyticcapacitors of samples E1 to E18 and samples C1 to C7 in the conditionsbeyond the guaranteed lifetime. Then, 30 samples of electrolyticcapacitors of each of samples E1 to E18 and samples C1 to C7 areproduced for carrying out an acceleration test.

The acceleration test is carried out in a state in which capacitorelement 12 is opened without using outer package 15 in order toaccelerate vaporization and volatilization of the solvent of electrolytesolution 16. That is to say, in the samples for the acceleration test,similar to the production procedure of each of the above-mentionedsamples, solid electrolyte layer 122 made of PEDOT is formed incapacitor element 12 if necessary and furthermore impregnated with apredetermined amount of each of the electrolyte solutions shown inTables 1 to 4. After that, capacitor element 12 is not accommodated incase 13 but maintained to be opened (exposed in atmosphere).

When capacitor element 12 is immersed in an anodization solution tocarry out repairing anodization, or when capacitor element 12 isimpregnated with a dispersion solution of an electroconductive polymer,in order to enhance the workability for the purpose of preventing theanodization solution or dispersion solution from attaching to leadwires, seal member 14 may be mounted on capacitor element 12.

Then, in the samples in this state, while a rated voltage is appliedbetween lead wires 11A and 11B, the samples are left in a constanttemperature chamber at a temperature of 125° C. for three hours. That isto say, in the acceleration test, while a rated voltage is appliedbetween anode foil 12A and cathode foil 12B, the samples are left under125° C. for three hours. As evaluation results of the acceleration test,measured initial properties and properties after the acceleration testare shown in Table 7. As the properties after the acceleration test, achange rate of capacitance, a change rate of ESR, a leakage currentvalue, and an occurrence rate of short circuit are calculated.Furthermore, change of the weight of electrolyte solution 16 before andafter the acceleration test is shown in Table 8.

TABLE 7 properties after acceleration test occurrence rate of shortchange in change in leakage current circuit sample capacitance (%) ESR(%) (μA) (%) E1 −39 35 6.1 0 E2 −34 32 3.5 0 E3 −32 32 0.6 0 E4 −21 310.5 0 E5 −16 29 0.7 0 E6 −38 34 2.5 0 E7 −30 29 0.5 0 E8 −28 28 0.6 0 E9−27 28 0.5 0 E10 −24 26 0.6 0 E11 −20 25 0.4 0 E12 −30 21 0.1 0 E13 −3020 0.1 0 E14 −31 15 0.1 0 E15 −35 32 0.6 0 E16 −33 30 0.6 0 E17 −20 260.5 0 E18 −16 25 0.5 0 C1 unmeasurable unmeasurable unmeasurable 100 C2unmeasurable unmeasurable unmeasurable 100 C3 −100 unmeasurable 0.8 0 C4−40 unmeasurable 0.7 0 C5 −35 unmeasurable 0.8 0 C6 −29 unmeasurable 0.70 C7 −22 unmeasurable 0.8 0

TABLE 8 properties after initial state acceleration test amount withinremaining amount initial electrolyte with respect to initial solutionelectrolyte solution volatile remaining rate of solvent low-volatilelow-volatile low-volatile solvent sample (wt %) solvent (wt %) solvent(wt %) (%) E1 70.0 5.0 4.9 98.0 E2 65.0 10.0 9.8 98.0 E3 60.0 15.0 14.898.7 E4 25.0 50.0 49.7 99.4 E5 0 75.0 74.6 99.5 E6 60.0 15.0 12.9 86.0E7 60.0 15.0 14.9 99.3 E8 60.0 15.0 14.9 99.3 E9 60.0 15.0 15.0 100 E1060.0 15.0 15.0 100 E11 60.0 15.0 15.0 100 E12 60.0 15.0 14.8 98.7 E1360.0 15.0 14.9 99.3 E14 60.0 15.0 14.9 99.3 E15 60.0 15.0 14.6 97.3 E1660.0 15.0 14.9 99.3 E17 60.0 15.0 15.0 100 E18 60.0 15.0 15.0 100 C175.0 0 0 — C2 — — — — C3 75.0 0 0 — C4 70.0 5.0 4.9 98.0 C5 65.0 10.09.8 98.0 C6 60.0 15.0 14.9 99.3 C7 25.0 50.0 49.7 99.4

Note here that being in an opened state at 125° C. for three hourscorresponds to being in a closed (sealed) state at 105° C. for 10000hours. This is a value that is much more than a guaranteed lifetime ofan electrolytic capacitor of 5000 hours at 105° C. This correlation canbe understood from the correlation between data of temperatures andspeeds at which each electrolyte solution vaporizes and volatilizes whencapacitor element 12 is in an opened state and data of temperatures andspeeds at which each electrolyte solution permeates and disperses fromseal member 14 when capacitor element 12 is tightly closed in case 13made of aluminum and seal member 14 of rubber packing.

As is apparent from Table 7, in hybrid-type electrolytic capacitors ofsamples E1 to E18, as compared with sample C1, in particular, theleakage current value and the occurrence rate of short circuit areremarkably reduced after acceleration test. As shown in Table 8, thesolvent of electrolyte solution A used in sample C1 is only volatileγ-butyrolactone and sulfolane, so that vaporization and volatilizationproceed under a high-temperature environment. As a result, after theacceleration test, the weight cannot be measured, and a solvent is lost.Consequently, a function of repairing a defective part in the dielectricoxide film by the electrolyte solution cannot be maintained, the leakagecurrent value is increased and the occurrence rate of short circuit ishigher.

On the other hand, since electrolyte solutions B to S used in samples E1to E18 contain polyalkylene glycol as a solvent, as shown in Table 8,vaporization and volatilization of the electrolyte solution aresuppressed even under a high temperature. Although not shown in Table 8,in any samples, a remaining amount of a volatile solvent after theacceleration test cannot be measured.

Thus, even after the acceleration test, in other words, even beyond theguaranteed lifetime, samples E1 to E18 maintain the function ofrepairing a defective part in the dielectric oxide film by theelectrolyte solution. Consequently, the leakage current value and theoccurrence rate of short circuit are suppressed. Therefore, samples E1to E18 have extremely high reliability.

Furthermore, as shown in the evaluation results of samples E3 to E5,when the content amount of polyethylene glycol contained in theelectrolyte solution is made to be at least 15 wt. %, an increase inleakage current and the occurrence rate of short circuit can be morereduced as compared with those of samples E1 and E2. In this way, whenthe content amount of polyethylene glycol is made to be at least wt. %,even if the electrolytic capacitor is exposed to a high-temperatureenvironment beyond the guaranteed lifetime, it is thought that theperformance and amount of an electrolyte solution sufficient to repairdefective parts occurring on the entire surface of dielectric layer 121can be maintained. Therefore, an excellent short-circuit resistanceproperty can be ensured.

Furthermore, in samples E3, and E6 to E11, the molecular weight ofpolyethylene glycol contained in the electrolyte solution is changed.From the results of samples E3, E7, E8, and E9, it is shown that whenthe molecular weight of polyethylene glycol is in a range from 300 to1000, inclusive, the increase in leakage current and the occurrence rateof short circuit can be particularly reduced. When the molecular weightof polyethylene glycol is in a range from 300 to 1000, inclusive, afunction of the solvent can be exhibited in a liquid state, lowvolatility is exhibited and the weight is hardly reduced even under ahigh-temperature environment as in an acceleration test. Therefore, aneffect of repairing a defective part in a dielectric oxide film by anonvolatile solute dissolved in the solvent can be maintained.

On the other hand, as shown in sample E6, even if the molecular weightof polyethylene glycol is 200, a function of a liquid-state solvent canbe exhibited. However, under a high-temperature environment,polyethylene glycol is vaporized and volatilized gradually although veryslightly as compared with volatile solvents such as γ-butyrolactone andsulfolane. In other words, among samples E1 to E18, a sample having thesmallest remaining rate of the low-volatile solvent is sample E6. Evenin this case, the leakage current and the occurrence rate of shortcircuit are remarkably reduced as compared with those of sample C1.Therefore, electrolyte solution 16 may have a composition so that atleast 86% of the low-volatile solvent remains after the electrolyticcapacitor is left under 125° C. for three hours while outer package 15is opened and a rated voltage of the electrolytic capacitor is appliedbetween lead wires 11A and 11B.

Note here that this example describes a case in which polyethyleneglycol having a molecular weight of 200 is used as the low-volatilesolvent. However, any other low-volatile solvents may be used as long asat least 86% of the low-volatile solvent remains after the accelerationtest. Furthermore, since the volatility of the solvent is affected byinteraction with respect to other components contained in theelectrolyte solution, the remaining rate may be achieved by a factor ofcomponents of the electrolyte solution other than the physical propertyof the low-volatile solvent itself.

On the other hand, as shown in samples E10 and E11, when the molecularweight of polyethylene glycol is increased to 1500 and 2000, the solventshows low volatility and the weight thereof is hardly reduced even undera high-temperature environment. However, viscosity is extremelyincreased and the impregnation property with respect to capacitorelement 12 is lowered, and thus the effective capacitance rate is low.

That is to say, even in the case where the molecular weight ofpolyethylene glycol is 200 or less and in the case where the molecularweight of polyethylene glycol is 1500 or more, as compared with aconventional hybrid-type electrolytic capacitor, when the electrolyticcapacitor is exposed to a high-temperature environment beyond theguaranteed lifetime, it is possible to remarkably improve electricproperties and to reduce occurrence rate of short circuit. However, inorder to achieve a stably effective capacitance and an effect ofsuppressing the increase in leakage current and occurrence of shortcircuit, it is preferable that the molecular weight of polyethyleneglycol is in a range from 300 to 1000, inclusive.

Furthermore, as shown in samples E15 to E18, when polypropylene glycolis used as a low-volatile solvent contained in the electrolyte solution,the same effect can be achieved as in the case where polyethylene glycolis used. That is to say, after the acceleration test, in other words,even beyond the guaranteed lifetime, a function of repairing a defectivepart in dielectric layer 121 can be maintained. As a result, the leakagecurrent value and the occurrence of short circuit can be suppressed.Thus, an electrolytic capacitor with extremely high reliability can beachieved.

Note here that as shown in sample E15, even if the molecular weight ofpolypropylene glycol is 100 or less, a function of a liquid statesolvent can be exhibited. However, under a high-temperature environment,polypropylene glycol is vaporized and volatilized gradually althoughvery slightly as compared with volatile solvents such as γ-butyrolactoneand sulfolane.

Furthermore, as shown in sample E18, when the molecular weight ofpolypropylene glycol is 6000 or more, the solvent shows low volatilityand the weight thereof is hardly reduced even under a high-temperatureenvironment. However, viscosity is extremely increased and theimpregnation property with respect to capacitor element 12 is lowered,and thus the effective capacitance rate is low.

Therefore, similar to the case of polyethylene glycol, in order toachieve a stably effective capacitance and an effect of suppressing theincrease in leakage current and occurrence of short circuit, it ispreferable that the molecular weight of polypropylene glycol is in arange from 200 to 5000, inclusive.

Furthermore, electrolyte solution M used in sample E12 contains boricacid in a component element, and electrolyte solution N used in sampleE13 contains pyromellitic acid in a component element. In addition,electrolyte solutions M and N are formed so that the ratio of the acidand the base contained in the solute and additives dissolved in thesolvent shows that the acid is more than the base, and they are incontact with the circumference of PEDOT of solid electrolyte layer 122.That is to say, components dissolved in the low-volatile solvent includea base and an acid more than the base. Therefore, electrolyte solutionsM and N can suppress dedoping of polystyrene sulfonic acid as the dopantcontained in PEDOT. Furthermore, since the solvent is low-volatile, evenafter the acceleration test, that is, even beyond the guaranteedlifetime, the effect against dedoping can be maintained. As a result, insamples E12 and E13, the change of ESR is suppressed. In other words,samples E12 and E13 exhibit extremely high reliability.

Furthermore, in sample E14, electrolyte solution O contains pyrogallolas an oxidation inhibitor, and it is in contact with the circumferenceof PEDOT of solid electrolyte layer 122. Therefore, electrolyte solutionO can suppress deterioration of PEDOT due to oxidation. Furthermore,since the solvent is low-volatile, after the acceleration test, that is,even beyond the guaranteed lifetime, the effect of suppressingdeterioration due to oxidation can be maintained. As a result, in sampleE14, the change of ESR is suppressed. That is to say, sample E14exhibits extremely high reliability.

An electrolytic capacitor of the present disclosure includes anelectrolyte solution, and a solid electrolyte such as anelectroconductive polymer. Therefore, the electrolytic capacitor of thepresent disclosure has a small size, a large capacitance, and a low ESR.Furthermore, the electrolyte solution has an effect of repairing adefective part occurring in a dielectric layer provided on the surfaceof the anode foil. The electrolyte solution of the electrolyticcapacitor of the present disclosure contains polyalkylene glycol orderivatives thereof having extremely low volatility. Therefore, even ifthe electrolytic capacitor is used under a high-temperature environmentof a maximum working temperature of 85° C. to 150° C. for a long timebeyond the guaranteed lifetime, a defective part occurring in thedielectric layer can still be repaired.

Therefore, the electrolytic capacitor of the present disclosure has asmall size, a large capacitance, and a low ESR, as well as can suppressthe increase in leakage current, and ensure an excellent short-circuitresistance property. Therefore, the electrolytic capacitor of thepresent disclosure is useful as electrolytic capacitors used in asmoothing circuit or a control circuit at the power supply output sideof electrical apparatus which require high reliability for a long time,for example, AV apparatus or electrical apparatus mounted on vehicles.

What is claimed is:
 1. An electrolytic capacitor comprising: a capacitor element having: an anode body having a dielectric layer thereon; and a cathode layer including a conductive polymer and in contact with the dielectric layer, and a liquid solution with which the capacitor element is impregnated, wherein: the liquid solution contains at least one of polyalkylene glycol and derivatives thereof, and a total weight content of polyalkylene glycol and derivatives thereof in the liquid solution is 15 wt % or greater with respect to a weight of the liquid solution.
 2. The electrolytic capacitor according to claim 1, wherein the liquid solution contains at least one of polyalkylene glycol and derivatives selected from the group consisting of polyethylene glycol, polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glyceryl ether, polypropylene glycol diglyceryl ether, polypropylene glycol sorbitol ether, polybutylene glycol, copolymers of ethylene glycol and propylene glycol, copolymers of ethylene glycol and butylene glycol, and copolymers of propylene glycol and butylene glycol.
 3. The electrolytic capacitor according to claim 1, wherein the liquid solution further contains at least one of γ-butyrolactone, ethylene glycol, and sulfolane.
 4. The electrolytic capacitor according to claim 1, wherein the liquid solution contains at least one of polyethylene glycol and derivatives thereof, both having a mean molecular weight from 300 to 1000, inclusive.
 5. The electrolytic capacitor according to claim 1, wherein the liquid solution contains at least one of polypropylene glycol and derivatives thereof, both having a mean molecular weight from 200 to 5000, inclusive.
 6. The electrolytic capacitor according to claim 1, wherein the liquid solution further contains at least one of diphenyl amine, naphthol, nitrophenol, catechol, resorcinol, hydroquinone, pyrogallol, trimellitic acid, pyromellitic acid, boric acid, boric-acid compounds, phosphoric acid, phosphoric-acid compounds, and complexes of mannitol and boric acid.
 7. An electrolytic capacitor comprising: a capacitor element having: an anode body having a dielectric layer thereon; and a cathode layer including a conductive polymer and in contact with the dielectric layer, and a liquid solution with which the capacitor element is impregnated, wherein the liquid solution contains at least one of polyethylene glycol and derivatives thereof, both having a mean molecular weight from 300 to 1000, inclusive, or at least one of polypropylene glycol and derivatives thereof, both having a mean molecular weight from 200 to 5000, inclusive.
 8. An electrolytic capacitor comprising: a capacitor element having: an anode body having a dielectric layer thereon; and a cathode layer including a conductive polymer and in contact with the dielectric layer, and a liquid solution with which the capacitor element is impregnated, wherein: the liquid solution contains at least one of polyalkylene glycol and derivatives thereof, and the liquid solution further contains at least one of diphenyl amine, naphthol, nitrophenol, catechol, resorcinol, hydroquinone, pyrogallol, trimellitic acid, pyromellitic acid, boric acid, boric-acid compounds, phosphoric acid, phosphoric-acid compounds, and complexes of mannitol and boric acid. 